Q: Can you identify these football-sized heavy citrus with concave centers? They are on a 12- to 14-year-old tree with 2- to 3-inch long thorns. The skin is quite thick, with an interior of pale yellow flesh with very harsh flavor – even when fruit is mature enough to fall off the tree.
Also, how many navel oranges should be culled from a tree’s branches, so that tree isn’t overweighted?
A: According to UC master gardener Annie Kempees, your mystery citrus is called a rough lemon. It’s commonly used as a rootstock by citrus growers. Preferred citrus varieties are grafted onto rough lemon rootstock because of its vigor. If a sucker is allowed to grow, it can rapidly take over the entire tree. As you’ve noticed, it has long thorns as well as sour fruit.
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You can use that fruit as you would regular lemons; they’re just not as juicy. The skin also can be used for zest.
As for thinning your oranges, here are some pointers to remember:
Most citrus will have many blossoms on the branches at the beginning of its growing season. Though many will be pollinated by bees, many others won’t and will simply fall off the tree.
From those that do get pollinated and form into fruit, several will fall from the tree in late spring. This is a natural occurrence called “June drop.” The remainder will grow through the summer and ripen in autumn and winter.
Whether or not to remove (or cull) navel oranges to avoid branch breakage is a personal choice. If you see several tight clusters of unripened fruit, feel free to thin them.
Occasionally, oranges will ripen and you will notice the branches needing some support. An especially heavily laden branch may be propped up by a heavy board with a V-shaped wedge cut into it and placed under that branch.
Cut the board long enough to successfully support the branch and to keep the board steadfastly on the ground. Take care not to damage the tree bark by rubbing off the outer skin and thus exposing it to insects and/or disease.
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